CN105355714A - Double-layer perovskite film with ferroelectric and semiconductor photovoltaic effects - Google Patents

Abstract

The invention discloses _a double _- layer _perovskite film _{with ferroelectricity} and semiconductor photovoltaic effect. _δ) , wherein A is Gd element, B is Ni element, and x=0.04～0.075, y=0.06～0.1, δ=0.05～0.3. The preparation method of the double-layer perovskite thin film is to first prepare a target material by a solid-phase sintering method, and then grow a uniform and dense thin film by a pulsed laser deposition method. The doped double-layer perovskite film of the present invention has the characteristics of ferroelectricity and N-type semiconductor. Compared with other ferroelectric films, it has a larger photovoltaic effect open circuit voltage (1.0-1.2V), and a larger photovoltaic effect. Effect short-circuit current density (13-40mA/cm ² ).

Description

A bilayer perovskite thin film with ferroelectricity and semiconducting photovoltaic effect

technical field

The invention belongs to the field of semiconductor materials, and in particular relates to a ferroelectric semiconductor thin film based on Bi ₂ FeCrO ₆ material doping.

Background technique

Photovoltaic materials are semiconductor materials that can directly convert solar energy into electrical energy, such as monocrystalline silicon, polycrystalline silicon, amorphous silicon, GaAs, GaAlAs, InP, CdS, CdTe, etc. Among them, monocrystalline silicon, polycrystalline silicon, and amorphous silicon have been mass-produced. Crystalline silicon, GaAs. At present, most semiconductor photovoltaic materials use the built-in electric field at the interface of the PN junction to spatially separate the photogenerated carriers to generate photocurrent, and the photovoltaic voltage generally does not exceed the bandgap width of the semiconductor. The ferroelectric material has anomalous photovoltaic effect, and its photovoltaic voltage is not limited by the crystal band gap (Eg), which can be 2 to 4 orders of magnitude higher than Eg, reaching 10 ³ to 10 ⁵ V/cm. Ferroelectric materials have the characteristics of high output photogenerated voltage and electric field regulation of photovoltaics, so they have broad application prospects in ferroelectric photovoltaic cells, optical drivers, and optical sensors.

Bi ₂ FeCrO ₆ is a multiferroic material, that is, it has both ferroelectricity and ferromagnetism. Ferroelectricity means that the material has spontaneous polarization, and within a certain temperature range, the direction of the spontaneous polarization dipole moment can change with the change of the applied electric field. Ferromagnetism means that the material has a spontaneous magnetic moment, and the spontaneous magnetic moment can be reversed with the change of the applied magnetic field. Studies have shown that Bi ₂ FeCrO ₆ also has semiconductor properties. Using first-principle calculations, Bi ₂ FeCrO ₆ is an indirect band gap material with a band gap of Eg=1.7eV, which can absorb most of the visible light. Lay a theoretical foundation for a photovoltaic material with high photoelectric conversion efficiency.

Chinese patent CN101255053 utilizes the solid solution technology based on the chemical pressure principle to realize the single-phase synthesis of Bi ₂ FeCrO _{6 ; 6} and other multiferroic materials to encode and store information. According to the article Bandgaptuning of multiferroic oxide solar cells (NechacheR, et al, Nature Photonics, 9, 61-67, 2015), the open-circuit voltage of the photovoltaic effect of Bi ₂ FeCrO ₆ is 0.56-0.84eV, and the maximum short-circuit current density of the photovoltaic effect of the single-layer film is 11.2mA/cm ² , In order to improve the photoelectric conversion efficiency of Bi ₂ FeCrO ₆ in practical applications, the photovoltaic performance needs to be further improved. Enhanced Electrical Properties of Bi _0.9 Gd _0.1 Fe _0.975 B _0.025 O _3±δ (B=Ni, Mn, Cu, Tian and V) ThinFilms (KimJW, et al, Ferroelectrics, 473, 129-136, 2014) reported that the common perovskite structure in BiFeO ₃ Doped with Gd and Ni elements, the Bi _0.9 Gd _0.1 Fe _0.975 Ni _0.025 O _3±δ film grown on the substrate Pt(111)/Ti/SiO2/Si(100) was prepared. Compared with the pure BiFeO ₃ film, its Both ferroelectric properties and leakage current are improved to some extent. So far, there has been no report on the preparation of bilayer perovskite ferroelectric thin films with N-type semiconductor characteristics by co-doping Gd and Ni elements on the basis of Bi ₂ FeCrO ₆ bilayer perovskite structure.

Contents of the invention

The purpose of the invention is to prepare a doped double-layer perovskite ferroelectric thin film with good photovoltaic performance.

Realize the technical scheme of the present invention is:

A double-layer perovskite photovoltaic thin film, the molecular formula of the composition of the thin film is Bi _2(1-x) A _2x (FeCr) _1-y B _2y O _6(1-δ) , wherein A is Gd element, B It is a Ni element, and x=0.04-0.075, y=0.06-0.1, and δ=0.05-0.3.

The photovoltaic thin film has N-type semiconductor characteristics, the carrier concentration is 10 ¹⁸ cm ^-3 to 10 ²⁰ cm ^-3 at 300K, and the carrier mobility is 2.2 cm ² ·V ^-1 ·s ^-1 to 300K. 25.6 cm ² ·V ^-1 ·s ^-1 .

Application of the above double-layer perovskite photovoltaic thin film in the preparation of PN junctions.

The direction of the photovoltaic current of the PN junction is opposite to that of the ferroelectric polarization of the film; the maximum photovoltaic current density of the PN junction is -36.2mA/cm ² or 17.5mA/cm ² .

Compared with prior art, the beneficial effect of the present invention is:

(1) In the present invention, by introducing Gd, Ni elements and oxygen vacancies, the double-layer perovskite film has N-type semiconductor properties, and the carrier concentration is 10 ¹⁸ cm ^-3 to 10 ²⁰ cm ^-3 at 300K, and the current is carried at 300K The submobilities range from 2.2 cm ² ·V ^-1 ·s ^-1 to 25.6 cm ² ·V ^-1 ·s ^-1 .

(2) Compared with the current ferroelectric materials, the thin film of the present invention has higher photovoltaic effect short-circuit current density and photovoltaic effect open circuit voltage.

(3) A PN junction composed of the N-type double-layer perovskite film of the present invention and P-type GaAs (or P-type GaN), the photovoltaic characteristics of the PN junction can be regulated by an external electric field, and the ferroelectric polarization can be reversed by an external electric field to thereby Change the direction and magnitude of the photovoltaic current.

Description of drawings

Figure 1 is a schematic diagram of the structure of a double-layer perovskite thin film device.

Fig. 2 is the X-ray diffraction spectrum of the Bi _1.9 Gd _0.1 (FeCr) _0.95 Ni _0.1 O _5.7 film of Example 1.

Fig. 3 is the X-ray diffraction spectrum of the Bi _1.85 Gd _0.15 (FeCr) _0.97 Ni _0.06 O _4.2 thin film of Example 2.

Fig. 4 is the X-ray diffraction spectrum of the Bi _1.92 Gd _0.08 (FeCr) _0.96 Ni _0.08 O _5.1 thin film of Example 3.

Fig. 5 is the hysteresis loop of three kinds of thin films of embodiment 1-3.

Fig. 6 is the transmission spectrum of three kinds of thin films of Examples 1-3.

Fig. 7 shows the current-voltage characteristics of the three kinds of films in Examples 1-3 after being polarized by +10V voltage.

Fig. 8 is the current-time curve of GaAs-Example 3 film heterogeneous PN junction under the action of an external electric field.

detailed description

The following examples are to further illustrate the present invention, but not to limit the scope of the present invention.

The direction of the electric field, the direction of the current, and the direction of ferroelectric polarization involved in the following embodiments all stipulate that the direction from the thin film to the substrate is positive, and the direction from the substrate to the thin film is negative.

As shown in Figure 1, the preparation process of the double-layer perovskite photovoltaic thin film of the present invention is as follows:

1. Target material preparation: Weigh Bi ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ and the selected doping element oxides according to a certain ratio, mix them evenly, put them into a ball mill jar for ball milling; mix evenly Press the powder into a cylinder, put it into a high-temperature furnace at 800-880 degrees Celsius and sinter for 1-3 hours;

2. Film preparation: a uniform and dense film is grown by pulsed laser deposition. Put the target material prepared in step 1 into the growth chamber, put the substrate into the growth chamber, first grow a conductive buffer layer on the substrate, the conductive buffer layer can be La _0.66 Sr _0.33 MnO ₃ or SrRuO ₃ ; and then grow Double-layer perovskite photovoltaic film layer, the atmosphere in the control chamber is pure oxygen, and the air pressure is 0.1Pa~10Pa, the temperature in the chamber is 670~690℃, the energy of a single laser pulse is 60~100mJ, and the growth frequency is 1~10Hz , The number of pulses is 5000~20000.

Example 1: growing a Bi _1.9 Gd _0.1 (FeCr) _0.95 Ni _0.1 O _5.7 (abbreviated as F1) film on a La _0.66 Sr _0.33 MnO ₃ buffer layer.

1. Target material preparation: mix Bi ₂ O ₃ , Gd ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , and Ni ₂ O ₃ powders evenly according to the molar ratio of 190:10:95:95:10, and put them into a ball mill The tank was ball milled at a speed of 300r/min for 12 hours, and the evenly mixed powder was pressed into a ceramic sheet, which was sintered at 850 degrees Celsius for 2 hours, and the excess powder was deposited around the ceramic sheet to avoid the volatilization of the Bi element.

2. Thin film preparation: put the target prepared in step 1 into the growth chamber, put the substrate into the growth chamber, and select a SrTiO ₃ (STO) single crystal substrate with (001) crystal plane; first grow a Layer conductive buffer layer La _0.66 Sr _0.33 MnO ₃ , increase the substrate temperature to 650 degrees Celsius, control the atmosphere in the cavity to be pure oxygen, and the pressure is 10Pa, the single laser pulse energy is 80mJ, the growth frequency is 2Hz, and the pulse number is 5000 .

Then grow a double-layer perovskite film, change the substrate temperature to 680 degrees Celsius, control the atmosphere in the cavity to pure oxygen, and the pressure is at 1Pa, the energy of a single laser pulse is 60mJ, the growth frequency is 5Hz, and the number of pulses is 20000.

3. Electrode preparation: A mask plate with a 100 μm diameter circular hole was pasted on the film prepared in step 2, and an electrode was prepared by a pulsed laser deposition method. The electrode material is ITO, the atmosphere in the control chamber is pure oxygen, and the pressure is 3Pa, the single laser pulse energy is 120mJ, grown at room temperature, the growth frequency is 5Hz, and the number of pulses is 6000.

4. Performance test: perform X-ray diffraction test on the prepared F1 thin film sample. The X-ray spectrum is shown in Figure 2. The F1 single crystal thin film grown on the SrTiO ₃ single crystal substrate has good lattice matching and no impurity phase.

The ferroelectric properties of the prepared F1 films were tested by a ferroelectric tester. The hysteresis loop is shown in Figure 5. The remanent polarization of the F1 film is 19.3 μC/cm ² , and the coercive electric field is 63.2 kV/cm.

The transmittance test was carried out on the prepared F1 film samples. The transmission spectrum is shown in Figure 6. It can be known from calculation that the forbidden band width of the F1 film is 1.53eV.

Photovoltaic performance tests were performed on the prepared F1 film samples. The thin film prepared in step 3 was first polarized by Keithley2635A digital source meter. Use +10V voltage to polarize for 1 second, remove the polarization voltage, and then use 100mW/ ^cm2 of light to vertically irradiate the upper surface of the polarized sample to test its photovoltaic performance. The photovoltaic characteristic curve is shown in Figure 7. It can be seen that the open circuit voltage of the F1 film is 1.02V, the short-circuit current density is 13.1mA/cm ² .

The electrical properties of the as-prepared F1 films were tested by a comprehensive physical property measurement system (PPMS). The F1 single crystal thin film has the characteristics of N-type semiconductor, the carrier concentration is 4.5×10 ¹⁸ cm ^-3 at 300K, and the carrier mobility is 2.4cm ² ·V ^-1 ·s ^-1 at 300K.

Example 2: growing a Bi _1.85 Gd _0.15 (FeCr) _0.97 Ni _0.06 O _4.2 (F2 for short) film on a SrRuO ₃ buffer layer.

1. Target material preparation: Mix Bi ₂ O ₃ , Gd ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , and Ni ₂ O ₃ powders evenly according to the molar ratio of 185:15:97:97:6, and put them into a ball mill The tank was ball milled at a speed of 300r/min for 12 hours, and the evenly mixed powder was pressed into a ceramic sheet, which was sintered at 835 degrees Celsius for 2 hours, and the excess powder was piled up around the ceramic sheet to avoid the volatilization of the Bi element.

2. Thin film preparation: put the target prepared in step 1 into the growth chamber, put the substrate into the growth chamber, and select the SrTiO ₃ single crystal substrate with (001) crystal plane; first grow a layer of conductive buffer on the substrate Layer La _0.66 Sr _0.33 MnO ₃ , increase the substrate temperature to 685 degrees Celsius, control the atmosphere in the cavity to be pure oxygen, and the pressure is at 10Pa, the single laser pulse energy is 80mJ, the growth frequency is 2Hz, and the number of pulses is 5000.

Then grow a double-layer perovskite film, change the substrate temperature to 670 degrees Celsius, control the atmosphere in the cavity to pure oxygen, and the pressure is 0.1Pa, the single laser pulse energy is 100mJ, the growth frequency is 1Hz, and the number of pulses is 20000.

3. Electrode preparation: A mask plate with a 100 μm-diameter hole was pasted on the film prepared in step 2, and an electrode was prepared by pulsed laser deposition. The electrode material is ITO, the atmosphere in the control chamber is pure oxygen, and the pressure is 3Pa, the single laser pulse energy is 120mJ, grown at room temperature, the growth frequency is 5Hz, and the number of pulses is 6000.

4. Performance test: perform X-ray diffraction test on the prepared F2 thin film sample. The X-ray spectrum is shown in Figure 3. The F2 single crystal thin film grown on the SrTiO ₃ single crystal substrate has good lattice matching and no impurity phase.

The ferroelectric properties of the prepared F2 films were tested by a ferroelectric tester. The hysteresis loop is shown in Figure 5, the remanent polarization of the F2 film is 24.5μC/cm ² , and the coercive electric field is 65.5kV/cm.

The prepared F2 film samples were tested for transmittance. The transmission spectrum is shown in Figure 6, and it can be known that the forbidden band width of the F2 thin film is 1.59eV through calculation.

Photovoltaic performance tests were performed on the prepared F2 film samples. The thin film prepared in step 3 was first polarized by Keithley2635A digital source meter. Use +10V voltage to polarize for 1 second, remove the polarization voltage, and then use 100mW/ ^cm2 of light to vertically irradiate the top surface of the polarized sample to test its photovoltaic performance. The photovoltaic characteristic curve is shown in Figure 7. It can be seen that the open circuit voltage of the F2 film is 1.06V, the short-circuit current density is 20.3mA/cm ² .

The electrical properties of the as-prepared F2 films were tested by a comprehensive physical property measurement system (PPMS). The F2 single crystal thin film has the characteristics of N-type semiconductor, the carrier concentration is 3.2×10 ¹⁹ cm ^-3 at 300K, and the carrier mobility is 6.5cm ² ·V ^-1 ·s ^-1 at 300K.

Example 3: growing a Bi _1.92 Gd _0.08 (FeCr) _0.96 Ni _0.08 O _5.1 (abbreviated as F3) film on a La _0.66 Sr _0.33 MnO ₃ buffer layer.

1. Target material preparation: mix Bi ₂ O ₃ , Gd ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , and Ni ₂ O ₃ powders evenly according to the molar ratio of 192:8:96:96:8, and put them into a ball mill The tank was ball milled at a speed of 300r/min for 12 hours, and the evenly mixed powder was pressed into a ceramic sheet, which was sintered at 865 degrees Celsius for 2 hours, and the excess powder was deposited around the ceramic sheet to avoid volatilization of the Bi element.

2. Thin film preparation: put the target prepared in step 1 into the growth chamber, put the substrate into the growth chamber, and select the SrTiO ₃ single crystal substrate with (001) crystal plane; first grow a layer of conductive buffer on the substrate Layer La _0.66 Sr _0.33 MnO ₃ , increase the substrate temperature to 650 degrees Celsius, control the atmosphere in the cavity to be pure oxygen, and the pressure is 10Pa, the single laser pulse energy is 80mJ, the growth frequency is 2Hz, and the number of pulses is 5000.

Then grow a double-layer perovskite film, change the substrate temperature to 670 degrees Celsius, control the atmosphere in the cavity to pure oxygen, and the pressure is 1Pa, the energy of a single laser pulse is 85mJ, the growth frequency is 1Hz, and the number of pulses is 20000.

3. Electrode preparation: A mask plate with a 100 μm diameter circular hole was pasted on the film prepared in step 2, and an electrode was prepared by a pulsed laser deposition method. The electrode material is ITO, the atmosphere in the control chamber is pure oxygen, and the pressure is 3Pa, the single laser pulse energy is 120mJ, grown at room temperature, the growth frequency is 5Hz, and the number of pulses is 6000.

4. Performance test: perform X-ray diffraction test on the prepared F3 thin film sample. The X-ray spectrum is shown in Figure 4, the F3 single crystal thin film grown on the SrTiO ₃ single crystal substrate has good lattice matching and no impurity phase.

The ferroelectric properties of the prepared F3 films were tested by a ferroelectric tester. The hysteresis loop is shown in Figure 5, the remanent polarization of the F3 film is 32.2μC/cm ² , and the coercive electric field is 69.1kV/cm.

The transmittance test was carried out on the prepared F3 film samples. The transmission spectrum is shown in Figure 6. It can be known that the forbidden band width of the F3 thin film is 1.45eV through calculation.

Photovoltaic performance tests were performed on the prepared F3 film samples. The thin film prepared in step 3 was first polarized by Keithley2635A digital source meter. Use +10V voltage to polarize for 1 second, remove the polarization voltage, and then use 100mW/ ^cm2 of light to vertically irradiate the upper surface of the polarized sample to test its photovoltaic performance. The photovoltaic characteristic curve is shown in Figure 7. It can be seen that the open circuit voltage of the F3 film is 1.18V, the short-circuit current density is 36.4mA/cm ² .

The electrical properties of the as-prepared F3 films were tested by a comprehensive physical property measurement system (PPMS). The F3 single crystal thin film has the characteristics of N-type semiconductor, the carrier concentration is 8.1×10 ¹⁹ cm ^-3 at 300K, and the mobility is 22.3cm ² ·V ^-1 ·s ^-1 at 300K.

Embodiment 4: F3 film is grown on p-type GaAs substrate, and GaAs-F3 heterogeneous PN junction is prepared.

1. Target material preparation: the F3 target material in Example 3 was selected.

2. Thin film preparation: put the F3 target into the growth chamber, put the substrate into the growth chamber, select the p-type GaAs single crystal substrate with (001) crystal plane, and the carrier concentration is 2.6×10 ¹⁸ cm ^-3 ; Grow a double-layer perovskite film on the substrate, change the temperature of the substrate to 670 degrees Celsius, control the atmosphere in the cavity to be pure oxygen, and the pressure is 1Pa; the energy of a single laser pulse is 85mJ, the growth frequency is 1Hz, and the number of pulses is 20000 .

3. Electrode preparation: A mask plate with a 100 μm diameter circular hole was pasted on the film prepared in step 2, and the top electrode was prepared by pulsed laser deposition. The top electrode material is ITO, the atmosphere in the control chamber is pure oxygen, and the pressure is 3Pa, the single laser pulse energy is 120mJ, grown at room temperature, the growth frequency is 5Hz, and the number of pulses is 6000.

A mask plate with a 100 μm diameter circular hole was pasted on the GaAs side of the sample to prepare the bottom electrode by pulsed laser deposition. The bottom electrode material is Pt, the single laser pulse energy is 200mJ, grown at room temperature, the growth frequency is 5Hz, and the number of pulses is 20000.

4. Photovoltaic performance test: first use Keithley2635A digital source meter to polarize the thin film prepared in step 3. Use different voltages to polarize for 1 second, remove the polarization voltage, and test the current of the PN junction under the alternating conditions of 2 seconds of darkness and 2 seconds of light (vertically illuminate the top electrode of the sample, and the light intensity is 100mW/cm ² ) for the polarized film. , the results are shown in Figure 8: there is no current under dark conditions, and current is generated under light conditions; the current characteristics of the PN junction will be affected after the polarization of the applied voltage, the direction of the light current is opposite to the direction of the polarization voltage, and the ferroelectric polarization is positive In the opposite direction, the maximum photovoltaic current of the PN junction is -36.2mA/cm ² , 17.5mA/cm ² .

Claims (4)

1. A double-layer perovskite photovoltaic film, characterized in that, the molecular formula of the film composition is Bi _2(1-x) A _2x (FeCr) _1-y B _2y O _6(1-δ) , wherein A is Gd element, B is Ni element, and x=0.04-0.075, y=0.06-0.1, δ=0.05-0.3. 2. The double-layer perovskite photovoltaic thin film according to claim 1, characterized in that the photovoltaic thin film has N-type semiconductor characteristics, and the carrier concentration is 10 ¹⁸ cm ^-3 to 10 ²⁰ cm ^-3 at 300K , the carrier mobility ranges from 2.2cm ² ·V ^-1 ·s ^-1 to 25.6cm ² ·V ^-1 ·s ^-1 at 300K. 3. The application of the double-layer perovskite photovoltaic film as claimed in claim 1 or 2 in preparing a PN junction. 4. application as claimed in claim 3, is characterized in that, the photovoltaic current of described PN junction is opposite to the ferroelectric polarization direction of thin film; The maximum photovoltaic current density of PN junction is-36.2mA/cm ² or 17.5mA/ cm ² .